Fix typo in FFmpeg description (meta-pytorch#991)

Author: SuperKenVery

docs/source/index.rst

@@ -11,7 +11,7 @@ We achieve these capabilities through:
 
 * Pythonic APIs that mirror Python and PyTorch conventions.
 * Relying on `FFmpeg <https://www.ffmpeg.org/>`_ to do the decoding / encoding.
-  TorchCodec uses the version of FFmpeg you already have installed. FMPEG is a
+  TorchCodec uses the version of FFmpeg you already have installed. FFmpeg is a
   mature library with broad coverage available on most systems. It is, however,
   not easy to use.  TorchCodec abstracts FFmpeg's complexity to ensure it is
   used correctly and efficiently.